1. Field of the Invention
The present invention relates to a signal processing apparatus and method for digital signals such as a digital image signal and a digital audio signal.
2. Description of the Related Art
Conventional signals such as a digital image signal and a digital audio signal are processed in a time region or in a frequency region. In the frequency region process, the component with the steady characteristic (the steady component) can be properly represented, while the component with the transient characteristic (the transient component) cannot be properly represented. In contrast, in the time region process, the component with the transient characteristic can be properly represented, while the component with the steady characteristic cannot be properly represented. The steady characteristic represents a stable repetitive change. On the other hand, the transient characteristic represents an independent single change.
As an example, FIGS. 1A and 1B show the case of a process in the time region. As shown in FIG. 1A, the component having the transient characteristic represents a wave form that largely changes on the time axis (impulse wave form). After sampling the wave form, it can be satisfactorily processed with for example several samples, i.e., dots in the wave form represent sampling points. In the case of a digital signal, the dots represent a discrete signal sequence with sampling values corresponding to the levels of sampling points. However, in the case shown in FIG. 1A and 1B, the transient characteristic can be represented by an analog signal wave. This applies to the following description. On the other hand, the component with the steady characteristic represents a wave form that gradually varies (flat wave form) on the time axis as shown in FIG. 1B. In this case, the feature of the wave form cannot be obtained with several samples. Thus, the steady characteristic cannot be satisfactorily processed.
In the frequency region, since the component with the steady characteristic includes one kind of single component or a few kinds of frequency components, it is represented as an impulse wave form as shown in FIG. 2A. On the other hand, the component with the transient characteristic is represented as a flat wave form as shown in FIG. 2B. As with the case of the time region, the impulse wave form more suitably represents the feature of the signal than the flat wave form.
A general signal wave form includes the component with the steady characteristic (flat) portions FL1, FL2, FL3, , . . . etc. and the component with the transient characteristic (impulse) portions IM1, IM2, . . . etc. on the time axis as shown in FIG. 3. Thus, when either the time region process or the frequency region process is performed, the feature of the signal cannot be correctly obtained. Thus, for the same signal, the process in the time region and the process in the frequency region should be performed, thereby increasing the process time and/or hardware scale.